1. Field of the Invention
This invention relates to an appliance and method for correcting a patient's malocclusion by encouraging relative jaw displacement, and more particularly, to an adjustable intraoral appliance that can deter an uncorrected bite, yet maintain a corrected bite.
2. Description of Related Art
Malocclusions are the improper positioning of the teeth and jaws. Generally, they are variations of the normal growth and development of the teeth and jaws that can affect a patient's bite, the ability to clean the teeth properly, gum tissue health, jaw growth, speech development and facial appearance. A bad bite can lead to a variety of problems, including abnormal wear of tooth surfaces, difficulty in chewing and excess stress on the supporting bone and gum tissue. Both heredity and environmental factors can play a role in the development of malocclusions. Some hereditary factors include the size and shape of the teeth and jaws, crowding of teeth, too much space between teeth, extra or missing teeth and cleft palate. Some environmental factors include tongue thrusting, dental disease and accidents, and habits like pacifier and finger/thumb sucking.
Malocclusions are categorized according to a class system. In Class I malocclusions, the jaws line up properly, but the teeth are crooked. Teeth are usually crowded, rotated and/or overlapped, and often are blocked out from alignment. In Class II malocclusions, the upper jaw appears to extend too far over the lower jaw. The lower or mandibular jaw bites in a retrusive position relative to the top or maxillary jaw. This misalignment is referred commonly as "buck" teeth, and more formally as overbite or overjet. Class III malocclusions are the opposite of Class II malocclusions; the lower jaw juts out further than the upper jaw, causing an underbite.
One of the problems encountered with a patient having a retrusive lower jaw (Class II malocclusion) is that the teeth of the lower jaw bite posterior to their normal correct biting positions against the upper teeth. Orthodontists have used a number of different devices over the years in an attempt to correct Class II malocclusions, including devices to hold the lower jaw forward from its retrusive position. After a period of time of wearing such a device, the bite hopefully becomes stable with the mandibular jaw in an advanced, "normal" position. This change is due both to migration of the teeth within the jaws, and to differential growth and remodeling of the jaws caused by wearing the device. In the field of orthodontics, a "normal" bite exists when the upper canine teeth bite distally relative to the lower canines, and the upper first molar mesial buccal cusp bites in the buccal groove between the lower first molar mesial and middle buccal cusps.
One approach to correct the overbite malocclusion is to wear an extraoral device, or headgear, which attaches via a face bow or j-hooks to the upper teeth by braces. The extraoral device exerts a force to the top or back of the head or the back of the neck through a tension device. This force, in turn, applies a posteriorly directed force to the upper teeth and jaw. Although such headgear offers one approach to correcting overbite or overjet, the device has several limitations. For example, because headgear is an extraoral device, it is highly visible and therefore has little patient appeal. Further, although headgear may be permanently attached, it usually is removable, and therefore, it often is difficult to ensure patient compliance.
Intraoral devices are also used to correct overbite. Intraoral devices overcome some of the disadvantages associated with extraoral devices. Some intraoral devices work exclusively on the teeth in the upper jaw, using the palate as an anchor. Other devices also can provide a posteriorly directed force to the upper jaw. Specific examples of such intraoral devices include the Jones jig and the Hilgers pendulum.
There are known other intraoral devices that attempt to correct overbite by both holding the lower jaw forward and tipping the upper jaw backward, while also moving the teeth in both jaws toward a corrected position. These devices apply both posteriorly directed forces to the upper teeth and jaw, and anteriorly directed forces to the lower teeth and jaw. Examples of such devices include Class II elastics, activators, bionators, Frankels, removable Herbsts, twin blocks and Korn appliances. Yet, these intraoral appliances are removable, limiting the effectiveness of such devices, similar to the external appliances, because of patient non-compliance.
Non-removable intraoral devices exist, which devices are permanently attached in the mouth. Specific examples of such permanent appliances include SAIF springs, Jasper jumpers, mandibulators and Herbst appliances. One of the limitations of this group of non-removable devices is that each of these devices creates some sort of permanent connection between the upper and lower teeth. Various types of linkages are used so that during natural closing and opening movements of the patient's jaws during speaking and chewing, the lower jaw is forced into an improved, forward position with respect to the upper jaw. The opening or closing forces of the jaw muscles are thus utilized to bring about the desired correction. A permanent change in the positional relationship of the jawbones occurs with use of such devices; therefore, this practice is termed "dental orthopedics". Some appliances for this purpose have employed rubber bands or springs arranged so that opening of the mouth tends to draw the lower jaw forward. Another approach to permanent appliances is the use of telescoping but rigid linkages between the upper and lower jaws that push the latter forward when the mouth is closed. Among other problems, this type of permanent connection appliance inhibits lateral jaw movement. During the months that the patient must wear this type of appliance, there are numerous occasions when side to side movement must be made. Any limitation of this mobility increases the discomfort of wearing the appliance.
Orthotic devices also are used in fields other than malocclusion correction, for example, in cases of temporomandibular joint (TMJ) dysfunction in order to advance the lower jaw for relief of pain, or to reduce clicking or locking. It is believed that such devices provide relief by decompressing the posterior ligaments of the condyle disk, by reducing the ability to clench the jaw-closing muscles when the lower jaw is forward, and by "recapturing" the displaced condyle disk onto the head of the condyle of the lower jaw. Devices currently being used to treat TMJ include a plastic orthotic portion or portions attached to the teeth and jaw with plastic indices attached to the opposing teeth so as to hold the lower jaw open and forward. However, such devices have several limitations, including that they are relatively bulky and do not allow the teeth of both jaws to be moved orthodontically while holding the lower jaw forward.
Additionally, orthodontic or orthopedic devices are used in the field of sleep disorders, for example, to treat snoring or obstructive sleep apnea. In the sleep disorder arena, it is known that snoring and obstructive sleep apnea usually are due, at least in part, to the tongue falling posteriorly during sleep, thereby pressing on the soft palate and reducing or blocking the airway. Traditional anti-snoring dental devices employ the principle of holding the lower jaw forward, thereby keeping the tongue out of the throat during sleep. Examples of such devices include bionators, activators, Herbsts and Jasper jumpers as mentioned above, as well as other devices such as the Snoreguard, SNOAR, NAPA, ASD and Feldman/Shapiro appliances. Although these devices usually offer some relief in the treatment of snoring or obstructive sleep apnea, they also include several disadvantages. For example, these devices are removable, raising patient compliance problems. In addition, several of the appliances are quite bulky. Further, many of the appliances result in morning jaw stiffness. Finally, these devices are difficult to wear if the teeth are being moved orthodontically.
Some specific examples of prior art references disclosing appliances addressed above include U.S. Pat. No. 4,382,783 to Rosenberg. Rosenberg discloses a linkage device used to join an upper molar and a lower molar on both sides of the mouth. An upper link 4 is hingedly attached at one end to a mounting block 3 extending from an upper molar, and hingedly attached at the other end to a cylinder 9 and a piston 5, which both serve as the lower link, attached to a lower molar mounting block. The linkage assembly of Rosenberg permanently links the maxillary and mandibular bones during use of the device. Rosenberg further discloses adjusting mechanisms including use of a spring 20 (FIG. 9), and the increase or decrease in the length of the lower link utilizing a piston 5 incorporating a stop 50, a threaded portion 52, and lock nut 48. (FIGS. 10 and 11)
U.S. Pat. No. 4,795,342 to Jones discloses a spring module orthodontic device having telescoping members for use in repositioning teeth. U.S. Pat. No. 4,969,822 to Summer discloses a telescopic oral orthopedic appliance comprising upper and lower channel-shaped attachment members 20, 22, connected to one another by a cylindrical sleeve 80 with rods 90, 92 extending therefrom, which rods 90, 92 hook to the upper and lower attachment members 20, 22, respectively. U.S. Pat. No. 5,352,116 to West discloses an adjustable bite corrector that is stretchable and has a degree of flexibility.
Of particular relevance in relation to the present invention, U.S. Pat. No. 5,848,891 (the "'891 device") to Eckhart et al. discloses an intraoral mandibular anterior repositioning appliance, commonly referred to as the MARA device. FIG. 1 of Eckhart et al. shows a typical overbite situation wherein the top jaw extends a distance x from the lower jaw. When the '891 device is installed in the patient's mouth, and the wearer attempts to close his/her mouth without properjaw adjustment, an abutment surface 60 of an L-shaped obstruction element 16 extends from a first member 12 attached to the patient's upper jaw, and rests atop an extending projection 24 connected to his/her lower jaw. As FIG. 1 of Eckhart et al. shows, the patient cannot close his or her mouth without properly aligning the jaws because at a point 66, the abutment surface 60 rests atop projection 24. As shown in Eckhart et al. in FIG. 2, the patient can only close his/her mouth when the bottom jaw slides forward relative to the top jaw so that the obstruction element 16 clears projection 24.
The MARA device embodies limitations that curtail its application in a number of situations. Its limitations are outlined in a widely distributed and respected manual specifically written for orthodontists and staff that install the MARA device in the patients' mouths. The manual, Clinical Management of the MARA, ("CMM"), includes an acknowledgment to Dr. Jim Eckhart, the inventor of the '891 device, for his significant contributions to the manual. The CMM exhaustively describes the preferred fitting procedures for the MARA device, and intermittently notes its limitations.
One disadvantage of the MARA device is that upon its initial fitting within the patient's mouth, the lower jaw is immediately repositioned forward relative the upper jaw. CMM, page 5. The patient is not provided with an accommodation period to become comfortable with weight and feel of the MARA itself, without any adjustment to the positioning of the jaws. Yet, this immediate dislocation of the jaws creates discomfort for the wearer, as he/she has no time to adjust to the MARA device alone (as a foreign device in the mouth), without the further unpleasantness associated with the shifted lower jaw. Presumably, the patient has had the malocclusion for some time, if not all his/her life, so the immediate jaw adjustment forced upon them by the MARA device is quite unnatural. It would be beneficial to provide an intraoral device and method that is designed to provide the patient a time to accommodate the new appliance, without any initial adjustment to the patient's jaws.
Further, the MARA device has only limited, discrete adjustment settings. For example, if a patient has a 12 mm overbite or overjet, the MARA device may only incorporate three adjustment settings, initially thrusting the lower jaw forward 4 mm, then after some time another 4 mm, and finally the last 4 mm. "A medium 4-5 mm Class II can be advanced the entire 4-5 mm initially. A severe 8-9 mm Class II should be advanced halfway (4-5 mm) at first." CMM, page 11. Even though it may not seem like a 4-5 mm distance is perceptible, any MARA user will readily admit each 4 mm adjustment alone is painful, much less several such adjustments.
The embodiment of the MARA device shown in FIGS. 1 and 2 of Eckhart et al. in fact provides no adjustment capability whatsoever, wherein the bottom jaw is forced to thrust forward until obstruction element 16 clears projection 24, and the malocclusion is fully corrected upon the initial fitting of the device, regardless how far the lower jaw must be thrust forward. FIG. 8 shows a device with quite limited, discrete adjustment settings, wherein the upper and lower obstruction elements can be adjusted via tracks 120, 140, and the adjustment secured by cotter pins or the like through holes 124, 148, respectively. These limited adjustment settings grant the patient little relief while his/her mandible is thrust forward the distance of the discrete adjustment required by the MARA device, as, for example, adjustment settings spaced 4-5 mm apart. It would be advantageous to provide an intraoral appliance that has a wide range of incremental and continuous adjustment settings, enabling smaller adjustment steps for the ease of the patient than are capable through use of the MARA device.
Since the MARA device has such limited adjustment settings, the device is subjected to enormous forces generated by the jaw muscles as they fight against the forward moving forces dictated by it. Therefore, the MARA device must be fabricated from sufficiently strong materials, or a large amount of material, so as not to break apart in the patient's mouth. As opposed to the MARA device, if a device had continuous adjustment settings so the forces borne by the device were less than those sustained by the MARA device (because the lower jaw is repeatedly moved forward only slightly), such an appliance could then be manufactured from less material or lighter weight material than the MARA device. A lighter appliance would aid in overall patient comfort, and lower costs of manufacturing such an appliance.
Not only do the forces borne by the MARA device necessitate a heavy construction, but they also typically compel the MARA device be secured to the patient's teeth via steel crowns placed on the teeth. Although bands are a preferred mounting assemblies for an intraoral appliance, bands cannot hold up to the above-described forces encountered by the MARA device. "[There are] breakage problems associated with using bands to fabricate the MARA . . . ." CMM, page 16, note. Crowns are the most intrusive type of mounting assemblies for the patient because they are harder to fit than bands, and decay can form under the crowns that would not be reachable by the clinician. Such decay is rarely associated with band use.
Additionally, adjusting the MARA device as shown in FIG. 8 of Eckhart et al. '891 patent only can be done by a dentist or like professional. Another improvement over the Eckhart et al. device would be an appliance designed to be easy to adjust, that if allowed by the dentist, the patient and/or a parent could adjust it without incurring the cost of numerous return trips to the dentist's office for adjustment.
It would also be advantageous to provide an intraoral appliance that can be adjusted by hand, with or without the need of specialized tools. Adjusting the MARA device can require removal of cotter pins, ligature wire and the like, which removal typically requires dental tools.
Further, use of the MARA can irritate the cheeks of the patient. "If the patient's maxillary arch is too narrow, the upper elbows on the MARA will be unable to hang buccally to the mandibular crowns without excessive buccal flaring, which causes . . . cheek irritation." CMM, page 12, note. Thus, an intraoral device incorporating cheek shields to protect the patient's cheeks from irritation would be beneficial.
Thus, it can be seen that there is a need for an improved growth appliance and method to correct malocclusions and the like by deterring an uncorrected bite, yet maintaining a corrected bite, a corrected bite being defined by the intraoral appliance.